How Amp-Hours Convert to Kilowatt-Hours
Amp-hours measure electrical charge, while kilowatt-hours measure energy. Amp-hours alone do not tell you how much energy a battery stores because the voltage must also be known. A 100 Ah battery at 12 volts stores a different amount of nominal energy than a 100 Ah battery at 48 volts.
This calculator converts battery capacity or electrical charge into watt-hours and kilowatt-hours using the nominal voltage you provide. It is useful for comparing batteries, estimating portable power capacity, sizing backup systems, and translating battery specifications into the energy units commonly used on electricity bills.
The result represents nominal stored energy. Real-world usable energy is usually lower because of depth-of-discharge limits, battery chemistry, temperature, age, wiring losses, and inverter efficiency. For example, a lithium battery may commonly be designed around a specific usable depth of discharge, while a lead-acid battery may require a larger reserve to avoid excessive wear.
Use the battery’s rated amp-hours and nominal voltage for a quick estimate. For a more realistic system estimate, multiply the nominal result by the expected usable fraction and efficiency of the complete system.
How to Calculate Amp-Hours to Kilowatt-Hours
Step One: Calculate Watt-Hours
Multiply the electrical charge in amp-hours by the voltage. This gives the battery’s nominal energy capacity in watt-hours.
watt-hours = amp-hours × voltage
Using the calculator’s default values:
100 Ah × 12 V = 1,200 Wh
Step Two: Convert Watt-Hours to Kilowatt-Hours
Divide watt-hours by 1,000 because one kilowatt-hour equals 1,000 watt-hours.
kilowatt-hours = watt-hours ÷ 1,000
Using the calculated watt-hour value:
1,200 Wh ÷ 1,000 = 1.2 kWh
Combined Formula
The two steps can be combined into one formula:
kilowatt-hours = (amp-hours × voltage) ÷ 1,000
For the default 100 Ah, 12 V example:
(100 × 12) ÷ 1,000 = 1.2 kWh
Estimating Usable Energy
To estimate usable energy, multiply the nominal capacity by the usable depth of discharge and system efficiency.
usable energy = nominal energy × usable fraction × efficiency
For example, assuming 80% usable capacity and 90% system efficiency:
1.2 kWh × 0.80 × 0.90 = 0.864 kWh
This final estimate is more practical than the nominal value when planning runtime or backup capacity.